Dietary Approaches to Stop Hypertension (DASH)

BACKGROUND:

The strong relationship between diet and blood pressure and the risk of hypertension has been well recognized. Currently, three specific diet-related factors have been recommended by the Joint National Committee on High Blood Pressure as a first-line approach in preventing and treating hypertension: caloric restriction for weight reduction, reduced consumption of alcohol, and lower sodium intake. Many studies, primarily observational, have shown significant associations between blood pressure and other diet-related factors, including micronutrients such as potassium, calcium, and magnesium; macronutrients such as type and amount of dietary fats, particularly polyunsaturated, and protein; and dietary fiber. However, results from individual, randomized, controlled clinical trials testing the effects of these nutrients on blood pressure have been inconsistent and equivocal. On the other hand, both observational and randomized intervention studies have consistently linked vegetarian dietary patterns to lower blood pressure.

To determine which specific dietary component may account for the blood pressure-lowering effect produced by vegetarian diets, numerous studies have examined individual micronutrients, macronutrients, and fiber. A large majority of cross-cultural and observational studies have shown a significant inverse association of blood pressure with the micronutrients, potassium, calcium, and magnesium, while the evidence linking dietary fiber to lower blood pressure comes primarily from studies on vegetarian and other high fiber diets. However, only a few of numerous clinical trials found that potassium or calcium supplements lower blood pressure. Randomized trials of magnesium supplementation generally have not shown a significant reduction in blood pressure. The few intervention studies of fiber supplements likewise generally have not demonstrated significant lowering of blood pressure. Pooled estimates from meta-analyses of potassium and calcium trials have reported small but significant reductions in systolic (potassium and calcium) and diastolic (potassium) blood pressure. All of these results are compatible with small effects of individual dietary components.

Only a few observational and intervention studies have demonstrated a relationship between the macronutrients, dietary fats or protein, and blood pressure. However, recent data analyses shown significant direct associations with saturated fat and dietary cholesterol, and inverse associations with protein intake.

Thus, an overall summary of the literature suggests that there is strong potential for a number of macronutrients and micronutrients to play an important role in reducing blood pressure. Testing dietary patterns rather than specific nutrients is a promising approach because it is not yet known which nutrients might be most effective in lowering blood pressure and because the effect of individual nutrients may be small. Testing dietary patterns would naturally include several nutrients that cumulatively are likely to lower blood pressure. Furthermore, most intervention studies which have not demonstrated decreases in blood pressure from individual nutrients used supplements rather than foods. Therefore, it may be important to test nutrients as components of foods and dietary patterns and not as isolated or processed nutrients.